"I guess my surprise was there weren't any surprises," said developer Christopher Allen, author of "iPhone in Action" and a founder of the iPhoneWebDev iPhone developer community. "If you know how to do iPhone development, then iPad development is very easy," said Allen. "They're very similar."

Apple released the iPhone 3.2 SDK, which includes an iPad emulator and iPad-specific extensions -- covering, for example, additional gestures such as swipes -- to the iPhone SDK, to registered iPhone developers on Jan. 28, the day after it announced the iPad.

"It is very similar to the iPhone SDK except it allows developers to create iPad apps to leverage the increased real estate -- the bigger screen size. Beyond that, there is nothing crazy nor really any new functionality," said Brandan Greenwood, director of client engagement for mobile solutions at iPhone application developer Amadeus Consulting.

The developer of Rackspace's cloud management application for the iPad, Michael Mayo, described the SDK as "just an update to the iPhone SDK."

Developers surveyed by InfoWorld are all focused on using that larger screen in their iPad applications. "There's a lot of things that the extra screen real estate gives you," Allen said.

Rackspace expects to rewrite its application for iPad, even if it does not have to do so, Mayo said. "I kind of am [rewriting it] because I want to add a lot more functionality," such as showing system status of the Rackspace cloud as whole, he said. The iPhone does not leave enough room for this but the iPad does, he explained.

"The hardest part is redesigning [the application]," said Mayo, where a developer must determine what the product will do and how it feels to the user in the new context.

Most iPhone apps already developed can run as is on the iPad, giving iPad users a large library of apps at the product's launch. The iPad includes a 2X virtual button that lets the iPhone apps run at 200 percent original size to fill the iPad screen; otherwise they run at the same size as on an iPhone. Several developers confimed that their iPhone apps ran as is on the iPad emulator.

"Right out of the gate the iPad already has 140,000-plus apps from the App Store. When iPhone came out there weren't that many apps right away and user were slower to adopt. Now it's easier for people to be jazzed about owning an iPad," Greenwood said.

In promoting the revised iPhone SDK, Apple's Web site notes that developers can create apps for both iPads and iPhones using a single binary. This lets developers use the same code to access capabilities that differ between an iPhone and an iPad, such as UI differences, without having to separately code for each device and then test to see which device is in use to determine which code segment to use.

"This is actually quite an old technology for Apple," Greenwood noted. "They've been doing it for a while, originally to enable [Motorola 680x0] apps and PowerPC apps to exist, later PowerPC apps and Intel 32-bit apps, and now Intel 32-bit apps and Intel 64-bit apps."

Allen anticipates a 4.0 OS upgrade for iPad and iPhone later this year, likely in June at the Apple World Wide Developers Conference, when Apple historically announces new iPhones. "There're some hints. Apple usually does a major rev every year," he said.